Tumorigenicity of malignant melanoma cells is well correlated with the production of plasminogen activators by these cells. Melanoma cells that have been treated with bromodeoxy-uridine, or that have been cocultured with a non-malignant line, fail to express plasminogen activator in vitro and do not produce tumors in syngeneic C57B1/6J mice. We are examining the relationship between the production of tumor cell secretory products such as plasminogen activator and the capacity of tumor cells to inhibit the host's inflammatory response.